Lubricant compositions of improved oxidation resistance



United States Patent 3,296,136 LUBRICANT COMPOSITIONS OF IMPROVEDOXIDATION RESISTANCE Daniel B. Eiciremeyer, Park Forest, and Tai S.Chao, Homewood, 11]., assignors to Sinclair Research, Inc., New York,N.Y., a corporation of Delaware No Drawing. Filed Nov. 13, 1963, Ser.No. 323,275 6 Claims. (Cl. 252-475) This invention relates toester-based lubricant compositions containing a novel combination ofadditive agents. More particularly the present invention relates toesterbased lubricant compositions which exhibit increased oxidationresistance.

Organic compounds, such as lubricating oils, undergo oxidation uponexposure to air. This process is accentuated by elevated temperaturessuch as occur in engines and other operating machinery. When suchorganic compositions are used as motor or machinery lubricants, theirstability is still further drastically reduced due to their contact withmetal surfaces which give up metallic particles into the lubricant. Suchabraded or dissolved metals or metal salts appear to act as oxidationcatalysts in the lubricant causing the formation of primary oxidationproducts which in turn cause further degradation of the organiccompounds present in the composition. Problems of this nature areencountered in mineral oils but appear to be particularly troublesome insynthetic oleaginous fluids exemplified by esters.

The development of modern high speed jet turbine aircraft enginesnecessitates the search for lubricants which are resistant to hightemperature oxidative degradation. Jet turbines are actuated by theenergy of a burning fuel and are used to drive compressors which providelarge amounts of air for the burning of the fuel. The combustion of thefuel provides the energy for driving the compressors with the remainderof the useful energy going into the propulsion of the aircraft. Jetturbine bearings are lubricated by pumping a lubricant to the bearingsfrom a reservoir in a closed system. The design of more powerful jetturbines has led to an increase in the lubricant reservoir temperatureand to greater difficulty in maintaining lubricant stability under themore severe conditions. For example, a lubricant which will operatesatisfactorily at a reservoir temperature of 250 F. may sludge badly,build up viscosity, develop high acidity and corrode metals at areservoir temperature of 440 F.

Thus jet turbine service requires a lubricant of superior thermal andoxidation stability as well as satisfactory physical characteristics interms of viscosity, flash point, volatility, and load carryingproperties. To arrive at such a lubricant it has been the generalpractice to add an antioxidant and other additives, such as foaminhibitors, anti-wear agents, etc. to a base fluid of suitableproperties.

Numerous oxidation and corrosion inhibitors have been found for use inlubricating compositions and many combinations thereof also have beentested. For instance, antioxidants such as phenothiazine;phenyl-a-naphthyL amine; S-ethyl-lO, 10-dipheuylphenazasiline; etc. arewell known in the art. The known inhibitors, however, are not adequateto prvoide the superior oxidation resistance now needed. Moreover, theeifectiveness of these known inhibitors is greatly impaired in thepresence of metal.

It is the object of this invention to provide an ester abse syntheticlubricant having superior resistance toward oxidative and thermaldegradation. It is a further object to protect and improve thisresistance against the detrimental effects of metals with the use ofsuitable additives.

3,296,136 Patented Jan. 3, 1967 The present invention provides animproved ester based lubricant composition containing small amountseflfective to retard oxidation, of each of a defined sulfur andnitrogen-containing organic compound and an arcmatic amine. The sulfurand nitrogen-containing organic compounds of my compositions are solublein the base ester oil to the extent present and have the formula:

wherein R is hydrogen, an aromatic radical of say up to 18 carbon atomsor an alkyl, including cycloalkyl, radical of, for instance, up to about18 carbon atoms; X is an amino or azo radical, that is, NR or -N=N; m is0 to 1; n is 1 to 2; and p is 1 to 2. In any given compound the Rradicals may be the same or difierently selected from the group ofradicals given; however, at least one of the R groups is other thanhydrogen and when m is O the R attached to the C(S) group is other thanhydrogen. Exemplary of the R aromatic radicals are pyridyl, phenyl andnaphthyl groups, which groups may be substituted with non-deleterioussubstituents such as one or more lower alkyl radicals. Also two Rgroups, say on opposite sides of the C(S)- radical, may be linkedtogether, especially when alkyl groups are involved. R may also be amixed radical, for instance of the aromatic alkyl type as in the case ofbenzyl.

The aromatic amine component of the invention is soluble in the esterfluid to the extent present and can be represented by the followinggeneral formula:

wherein Q is a monovalent hydrocarbon of 1 to 20 carbons, preferably 6to 12 carbon atoms, whose adjacent carbon atoms are no closer than 1.40A (i.e. a non-olefinic, non-acetylenic, monovalent hydrocarbon), and Qis an aromatic hydrocarbon radical of 6 to 12 or 16 carbon atoms. Thus Qcan be an alkyl group, including cyclokalyl or an aromatic group.Preferably, both Q and Q are aromatic and often at least one is a fusedring aromatic, e.g. naphthyl. Q and Q can be substituted withnon-interefering substituents such as alkyl groups and amine groups,preferably alkyl or aromatic amines, and Q and Q can be linked togetherby means of a non-interfering element such as carbon, sulfur and oxygen.lllustrative of suitable amines are phenothiazine, N-phenyltit-naphthylamine; dim-naphthyl amine); N,N'-diphenyl para-phenylene diamine;N,N-dioctyl para-phenylene diamine, N,N-heptylphenyl-para-phenylenediamine; diphenyl amine, N-butyl phenyl-(u-decyl) amine, di-betanaphthylamine, etc.

The lubricant composition of this invention includes as the majorcomponent a base oil which is an ester of lubricating viscosity whichmay be, for instance, a simple ester or compounds having multiple estergroupings such as complex esters, di or other polyesters, and polymeresters. These esters are usually made from monoand polyfunction-alaliphatic alcohols or alkanols, and aliphatic mono and poly carboxylicor alkanoic acids. Frequently, the alcohols and acids have about 4 to 12carbon atoms. The reaction product of a mono-functional alcohol and amonocarboxylic acid is usually considered to be a simple ester. Adiester is usually considered to be the reaction product of 1 mole of adicarboxylic acid, say of 6 to 10 carbon atoms, with 2 moles of amonohydric alcohol or of 1 mole of a glycol, for instance, of 4 to 10carbon atoms, with two moles of a monocarboxylic acid, e.g. of 4 to 10carbon atoms. The diesters frequently contain from 20 to 40 carbonatoms.

A complex ester is usually considered to be of the type XYZYX in which Xrepresents a monoalcohol residue. Y represents 'a dicarboxylic acidresidue and Z represents a glycol residue and the linkages are esterlinkages. Those esters, wherein X represents a monoacid residue, Yrepresents a glycol residue and Z represents a dibasic acid residue arealso considered to be complex esters. The complex esters often have 30to 50 carbon atoms.

Polymer esters or polyester bright stocks can be prepared by directesterification of dicarboxylic acids with glycols in about equimolarquantities. The poly esterification reaction is usually continued untilthe product has a kinematic viscosity from about 15 to 200 centistokesat 210 F and preferably 40 to 130 centistokes at 210 F.

Although each of these products in itself is useful as a lubricant, theyare particularly useful when added or blended with each other insynthetic lubricant compositions. These esters and blends have beenfound to be especially adaptable to the conditions to which turbineengines are exposed, since they can be formulated to give a desirablecombination of high flash point, low pour point, and high viscosity atelevated temperatures, and need contain no additives which might leave aresidue upon vol-atiliaztion. In addition, many complex esters haveshown good stability to shear. Natural esters, such as castor oil may beemployed and also be included in the blends, as may be small amounts ofa foam inhibitor such as a methyl silicone polymer, or other additivesor lubricant components to provide a particular characteristic, forinstance, extreme pressure or load carrying agents, corrosioninhibitors, etc., can be added.

The monohydric alcohols employed in these esters us ually contain about4 to 20 carbon atoms and are generally aliphatic. Preferably the alcoholcontains up to about 12 carbon atoms. Useful alkanols include butyl,hexyl, methyl, iso-octyl and dodecyl alcohols, C oxo alcohols andoctadecyl alcohols. C to C branched chain primary alcohols arefrequently used to improve the low temperature viscosity of the finishedlubricant composition. Alcohols such as n-decanol, 2-ethyl-hexanol, oxoalcohols, prepared by the reaction of carbon monoxide and hydrogen uponthe olefins obtainable from petroleum products such as diisobutylene andC olefins, ether alcohols such as butyl carbitol, tripropylene glycolmono-isopropyl ether, dipropylene glycol monoisopropyl ether, andproducts such as Tergitol 3A3 which has the formula C13H27O(CH2CH2O)3H,are suitable alcohols for use to produce the desired lubricant. If thealcohol has no hydrogens on the beta carbon atoms, it is neo-structured;and esters of such alcohols are often preferred. In particular, theneo-C alcohol--2,2,4-trimethyl-pentanol-1gives lubricating diesters orcomplex esters suitable for blending with diesters to produce lubricantswhich meet stringent viscosity requirements. Iso-octanol and iso-decanolare alcohol mixtures made by the x0 process from C 43 copolymerheptenes. The cut which makes up iso-octanol usual-1y contains about 17%3,4-dimethylhexanol; 29% 3,5-dimethylhexaaol; 25% 4,5-dimethylhexanol;1.4% 5,5-dimethylhexanol; 16% of a mixture of 3-methylheptanol andS-ethylheptanol; 2.3% 4-ethylhexanol; 4.3% a-alkyl alkanols and 5% othermaterials.

Generally, the glycols contain from about 4 to 12 carbon atoms; however,if desired they could contain a greater number. Among the specificglycols which can be employed are 2-ethyl-l,3-hexanediol, 2-propyl-3,3-

heptanediol, 2 methyl 1,3 pentanediol, 2-butyl-1,3-

butanediol, 2,4 diphenyl 1,3 butanediol, and2,4-dimesityl-1,3-butanediol. In addition to these glycols, etherglycols may be used, for instance, where the alkylene radical contains 2to 4 carbon atoms such as diethylene glycol, dipropylene glycol andether glycols up to 1000 to 2000 molecular weight. The most popularglycols for the manufacture of ester lubricants appear to bepolypropylene glycols having a molecular weight of about 100-300 and2-ethyl hexanediol. The 2,2-dimethyl glycols, such as neopentyl glycolhave been shown to impart heat stability to the final blends. Minoramounts of ether glycols or other materials can be present as long asthe desired properties of the product are not unduly deleteriouslyaffected.

One group of useful monocarboxylic acids includes those of 8 to 18 oreven 24 carbon atoms such as stearic, l-auric, etc. The carboxylic acidsemployed in making ester lubricants will often contain from about 4 to12 carbon atoms. Patent No. 2,575,195, and include the aliphatic dibasicacids of branched or straightchain structures which are saturated orunsaturated. The preferred acids are the saturated aliphatic carboxylicacids containing not more than about 12 carbon atoms, and mixtures ofthese acids.

sebacic acids and isosebacic acid which is a mixture of a-ethyl subericacid, oc,oz'-diethyl adipic acid and sebacic.

acid. This composite of acids is attractive from the viewpoint ofeconomy and availability since it is made from petroleum hydrocarbonsrather than the natural oils and fats which are used in the manufactureof many other dicarboxylic acids, which natural oils and fats arefrequently in short supply. The preferred dibasic acids are sebacic andazelaic or mixtures thereof. Minor amounts of adipic used with a majoramount of sebacic may also be used with advantage.

The ester base oils to which incorporation of the additive combinationof the invention is particularly advantageous are the oils commonlyreferred to as neopentyl polyol polyesters, i.e. having more than oneester group. These are the esters of aliphatic carboxylic acids, gen

erally monoalkanoic acids, of about 4 to 12 carbon wherein n is 0 to land R is a lower alkyl group, preferably of about 1 to 4 carbon atoms,which can be straight or branched chain, or a hydroxy methyl group.These esters can be made by reacting a mole of the alcohol with about 2moles up to the stoichiometric equivalent of the carboxylic acid.

Illustrative of polyhydric alcohols free of beta hydrogen are neopentylglycol, trimethylolethane, ,trimethylolpropane, pentaerythritol,dipentaerythritol, 2-butyl-2-ethyl-1, 3-propanediol, etc. Suitablealiphatic carboxylic acids with which the polyhydric alcohols free ofbeta hydrogen may be esterified are n-butyric acid, isobuty-ric acid,npentanoic acid, isopentanoic acid, n-heptanoic acid, isoheptanoic acid,n-octanoic acid, isooctanoic acid, pelargonic acid, n-decanoic acid,lauric acid, myristic acid, stearic acid, n-dodecanoic acid, valericacid, n-hexabutyric acid, etc.

The additives of the invention are incorporated in the base oil inamounts sufiicient to retard oxidation of the oil, and theconcentrations employed for optimum results may depend on the particularbase oil and second additive component selected. Ordinarily about 0.05to t 5%, preferably about 0.1 to 2%, by weight of each of thesulfur-nitrogen compound and the amine additive corn- Suitable acids aredescribed in U.S.

wnaphthylamine, Test No. 8; base fluid A plus 0.1% thionicotinamide,Test No. 2; and base fluids A and B plus 1% or 0.5%, respectively, ofN-phenyl-a-naphthylamine and a given amount of the sulfur-nitrogenadditive of the 2. The lubricant composition of claim 1 wherein Q is anaromatic hydrocarbon radical and Q and Q each has 6 to 12 carbon atoms.

3. The lubricant composition of claim 1 wherein the present inventtion,the remaining tests through Test No. 5 sulfur-nitrogen compound ispresent in an amount of 21. In Test No. 22 the lubricant was the same asthat of about 0.1 to 2% by weight and the aromatic amine is Test No. 3,except for the addition of 1% of 2,2'-dipyridylpresent in an amount ofabout 0.1 to 2% by weight. amine; and in Tests Nos. 23 and 24, the fluidof Test N0. T l ri an composition Of claim 1 wherein the 22 containedthe stated amount of the identified additional ester base fluld s anester of an elkanol havmg the SFN wmpounds. eral formula:

The times to the end of the inhibition period and to the j: end of thetest are designated Ti and Tt, respectively, and HOCHz- CH2-OCH2 OH2OHthe volume of oxygen absorbed is designated Vt. L 1!; J,

TABLE I Test No. Base blend Sulfur-Nitrogen (S-N) Additive Wt. percentTi (min.) Tt (min) Vt (1111.)

S-N Additive None 5 41 2, 500 Thionicotinamide 0. 1 10 80 2, 500 one 91128 2,500 s-Di-n-butylthiourea 0. 1 108 153 2, 500 Ethylenethiourea 0. 1439 1, 370 2thiobenzoy1amino-4-rnethylpyr1 0. 3 420 1, 240N-phenyl-N-2-pyridylthiourea 0. 23 168 276 2, 500 None 163 2. 500s-Dimethylthi0urea 1. 0 293 2, 500 s-Di-n-buty1thiourea 1. 0 382 2, 500s-Diphenylthiourea 1. 0 492 2, 500 s-Diphenylthiourea 0. 1 202 2, 500N-phenyl-N-2-pyridylthiourea 0. 2 406 2, 500 N -phenyl-N-l-naphthylthiourea. 0. 5 365 2, 500 s-Dl-p tolythiourea 0. 5 3992, 500 N-phenyl-N-laurylthiour 1. 0 316 2, 500 Diphenylthiocarbazone. 0.2 252 2, 500 2-thiobenzoyl-aminopyridine. 0. 5 349 2. 500N,N-di1auryl-dithiooxarn.ide 0. 5 327 2, 500 1,1-diphenyl-2-tbiourea 0.1193 2,500 s-Dibenzylthiourea 0. 5 279 2, 500 m 353 2,5002-thiobenzoylarnino--methylpyridine 0.15 1, 200 2, 500 Thiom'cotin'tmide0. 5 466 1, 373

1 Test Conditions: 450 F., 1 cu. ft. O /hL, 75 g. sample.

2 Base Fluid A: An essentially complete ester of pentaerythritol and amixture of alkanoic acids containing an average of seven carbons permole and characterized by an acid number of 0.01, a sap. number of 400and kinematic viscosities at 210 F. of 5.30 cs. and at 100 3 Base FluidB: diisooctyl azelate; 80% complex ester from neopentyl glycol, azelaicacid and isooctyl alcohol, mole ratio approx. 112:2.

We claim:

1. A lubricant composition consisting essentially of a major amount ofan ester base fluid of lubricating viscosity and small amounts of eachof an ester base fluid-soluble compound having the following structuralformula:

R is selected from the group consisting of hydrogen, alkyl radicals ofup to 18 carbon atoms, phenyl, naphthyl References Cited by the Examinerand pyfi UNITED STATES PATENTS X is selected from the group consistingof NR1 a d 2,201,170 5/ 1940 Hanford 260-3 13 2,242,621 5/ 1941 Schulzeet a1 44-74 0 to 13 2,302,552 4/1942 Johnson 25247 "1 and 2,322,1846/1943 White 252-47 P 2,373,049 4/1945 Pedersen 252-47 with the provisothat at least one R 1s other than hydrogen 2 396 156 3/1946 Clarkson andwhen m is 0 the R attached to the CS- group i 2484257 10,1949 W t o 25247 other than hydrogen, and an ester base fluid-soluble arO- n maficamine having the general formula: 2,657,984 10/ 1953 Braithwarte 2S247Q-N-H FOREIGN PATENTS wherein Q is a non-olefinic, non-acetylenicmonovalent 550 340 7 19 5 d hydrocarbon radical of 1 to 20 carbon atomsand Q is an 601,174 7/1960 aromatic hydrocarbon radical of 6 to 16carbon atoms, said amounts being effective to retard oxidation of saidester base fluid at temperatures in excess of 400 F., and said esterbase fluid being an ester of an alkanol of 4 to 20 carbon atoms and analkane carboxylic acid of 4 to 18 carbon atoms.

DANIEL E. WYMAN, Primary Examiner.

L. G. XIARHOS, Assistant Examiner.

1. A LUBRICANT COMPOSITON CONSISTING ESSENTIALLY OF A MAJOR AMOUNT OF ANESTER BASE FLUID OF LUBRICATING VISCOSITY AND SMALL AMOUNTS OF EACH OFAN ESTER BASE FLUID-SOLUBLE COMPOUND HAVING THE FOLLOWING STRUCTURALFORMULA:
 4. THE LUBRICANT COMPOSITON OF CLAIM 1 WHEREIN THE ESTER BASEFLUID IS AN ESTER OF AN ALKANOL HAVING THE GENERAL FORMULA: